Heat shock protein (hsp) gp96 (glycoprotein 96), also called as grp94 (glucose-regulated protein 94), is a member of hsp90 family which located on endoplasmic reticulum (ER) membrane of cells, the protein has about 96 KDa of molecuar weight and plays an important role in cellular protein folding and transportation. Recent studies have showed that gp96 is also expressed on the surface of some tumor cells. Gp96 possesses two conserved domains, the C-terminal is a polypeptide-binding domain which can bind a variety of polypeptides with 5-25 amino acids, and the N-terminal is a ATP-binding domain with ATPase activity. Heat shock protein hsp78, a member of hsp70 family in cytoplasma, has about 78 KDa of molecular weight and plays an important role in cellular protein folding and transportation. Hsp78 can bind to a variety of short peptides as molecular chaperone, it has two functional domains: the N-terminal domain with ATPase activity and the C-terminal domain which can bind to polypeptide substrate.
Recent studies demonstrated that immunization with gp96 and hsp78 purified from tumor tissues or cells infected by virus could elicit a specific immunological rejection response against the tumors or viruses. A further study showed that gp96 and hsp78 can bind to all peptide libraries generated in the cells including antigenic polypeptides, this specific immunological response is based on the polypeptides bound to gp96 and hsp78 not the heat shock protein itself, gp96 and hsp78 from tumor tissues or cells infected by virus normally bind to tumor or virus specific polypeptides, gp96 and hsp78 can present the antigenic ploypeptides bound by them to major histocompatibility complex (MHC) molecules and activate cytotoxic T lymphocyte (CTL) to elicit cell immunological response generated by organism. Since gp96 and hsp78 play an important role in antigen presentation in the cells, gp96-ploypeptide complex and hsp78-polypeptide complex can be used to prevent autogenous tumors and some infectious diseases.
Pramod K. Srivastava from University of New York, USA, applied for 6 patents (U.S. Pat. Nos. 6,017,544, 6,017,540, 6,007,821, 5,837,251 and 5,830,464) in USA based on his studies. These patents mainly relate to the use of a complex of heat shock protein (hsp) non-covalently bound to antigen molecular for treating primary and transferred tumors as well as infectious diseases, and activating immunological response generated by organism, wherein the antigen moleculars include the esoteric polypeptides bound to hsp, and also include exoteric antigens or immunogenic fragments that can form complex with hsp in vitro. Hsp mainly comprises hsp70, hsp90 and gp96 protein.
It has been demonstrated that gp96 and hsp78 can bind antigenic polypeptides such as antigenic peptide of vesicular stomatitis virus, ovalbumin antigenic epitope peptide restricted by mouse H-2Kb and an Ld-restricted CTL epitope peptide of a mouse leukemia. Up to now, however, no antigenic ploypeptides bound to hsps have yet been identified in patients tissues infected by virus.
It is estimated that about 350 million individuals worldwide have been infected by HBV, and in China alone the number is about 120 million. HBV is the leading cause of chronic hepatitis, cirrhosis and liver cancer, so it is a kind of infectious diseases that severely disserve the life health of Chinese. The probability of liver cancer developing from hepatitis B is also very high. The HBcAg-positive hepatocytes account for 62.5% in total HCC cells and 29.2% in the totally adjacent liver cells. Cell immunological response elicited by CTL is a major pathway to clear virus and cure hepatitis B. In the patients infected by hepatitis B virus, the HBV antigenic ploypeptide is presented to MHC I molecular after process, and activates specific CTL to elicit cell immunological response. Now, some CTL epitopes on the HBV core protein have been identified, including HLA-A2 restricted HBcAg18-27, HLA-A11 restricted HBcAg88-96 and like. Therefore, it is very important to develop a novel drug for the prevention and treatment of HBV associated hepatitis and primary hepatocellular carcinomas, especially a drug that can elicit actively CTL immunological response generated by organism.